The present invention relates to epoxy resins and their use in electronics packaging applications. In a particular aspect, the invention relates to hydrophobic epoxy resins. In another aspect, the present invention relates to high Tg resins.
Epoxy based resins have a variety of applications in adhesives, potting compounds, laminates, composites, coatings, etc. Epoxy compounds with more than one epoxy functional group per molecule can readily be polymerized via a ring-opening, step-growth, addition mechanism to yield thermoset compositions. Epoxy resins can be homopolymerized in the presence of a suitable catalyst or via the further addition of a curing agent (e.g., amines, mercaptans, phenols, anhydrides, and the like). These cure mechanisms, in either case, do not result in the release of any volatiles, which is critical for void-free cure. Furthermore, epoxy resin thermosets are noted for their low cure shrinkage, corrosion resistance, and good electrical properties. Epoxy thermosets can also be formulated to yield tough, adherent compositions.
Epoxy resin types include glycidyl ether, aliphatic and cycloaliphatic oxirane compounds. Cycloaliphatic epoxy thermosets, in particular, are noted for their high glass transition (Tg) temperatures. High Tg thermosets are desirable since they can be used in more demanding (e.g., high temperature) applications without a significant loss of physical properties. For examples of cycloaliphatic epoxy thermosets, reference is made to Kataoka, et al. (U.S. Pat. No. 5,783,639, hereinafter xe2x80x9cthe ""639 patentxe2x80x9d). Cycloaliphatic epoxy resins have a further advantage over most glycidyl ether type resins in that they are virtually free of ionic chloride residues. Residual chloride ion contamination, by virtue of its tendency to promote corrosion of metal traces, cannot be tolerated in electronic applications at levels much greater than about ten parts per million. The glycidyl ether type epoxy resins routinely have several times this level of extractable chloride ion, and often require the use of intensive clean-up efforts to achieve acceptable levels. The cycloaliphatic resins are further distinguished over the aliphatic epoxies by their higher reactivity and ability to yield high Tg thermosets. Despite their high Tg, ionic purity, and reactivity advantages, presently commercially available cycloaliphatic epoxy resins do not yield hydrophobic thermosets. Hydrophobicity results in a low moisture content, which is desirable because moisture can cause popcorning (i.e., violent release of volatiles). Furthermore, presently commercially available cycloaliphatic epoxy resins are also noted for their susceptibility to hydrolysis in the presence of hot and humid environments. This hydrolysis problem can lead to catastrophic adhesive failure in the presence of moisture.
Accordingly, there is still a need in the art for epoxy resins that have the advantages imparted by cycloaliphatic epoxies yet which are hydrophobic in nature and have reduced susceptibility to hydrolysis.
The present invention provides novel epoxy compounds which, when employed in resins, overcome the problems of hydrophilicity and hydrolytic instability associated with commercially available cycloaliphatic epoxies while maintaining the advantages of high Tg, ionic purity, and cure speed. Invention epoxy compounds are based on polycyclic hydrocarbon backbones. Specifically, invention epoxy compounds are derived from oligomers of cyclopentadiene and related vinyl and/or divinyl compounds capable of undergoing Diels-Alder cycloaddition.
Invention epoxy compounds may be cured to yield thermosets via the addition of suitable curing agents and catalysts. Certain cationic initiators can be used to promote efficient homopolymerization of these epoxy compounds. The latter cure method is particularly desirable where the lowest possible dielectric constant and moisture uptake is required. Another advantage of invention materials is that epoxy resins having much lower viscosity can be made using invention epoxy compounds than by employing prior art epoxy compounds. Invention compounds may be used as the sole epoxy component or they may be added to other epoxy compounds to enhance the ultimate performance characteristics. In a further aspect of the present invention, polycycloaliphatic epoxy and glycidyl ether epoxy functional groups may be combined in the same molecule. This capability can be especially useful in applications where it is desirable to have different levels of reactivity (such as for the formation of B-staged adhesives).